“…Modulation spectroscopy is a popular means of analysing critical point (CP) structures in semiconductors [3]. Some modulation techniques, such as electroreflectance (ER) [4][5][6][7][8][9][10], photoreflectance (PR) [11,12], electroabsorption [13], piezoreflectance (PzR) [14,15] and thermoreflectance (TR) [16], have been used to investigate CP structures in Ga 0.5 In 0.5 P and consequently, its electronic band structure. The temperature dependence of the E 0 /(E 0 + 0 ) energies for Ga 0.5 In 0.5 P has also been extensively investigated using various techniques, such as ER [6], PR [11], PzR [15], photoluminescence [6,[17][18][19][20][21] and photoluminescence excitation spectroscopy [18,21].…”